In the field of counterintelligence, a double agent (also double secret agent) is an employee of a secret intelligence service, whose primary purpose is to spy on a different target organization, but who, in fact, is a member of the target organization.[1]

Double agentry may be practiced by spies of the target organization who infiltrate the controlling organization, or may result from the turning (switching sides) of previously loyal agents of the controlling organization by the target. The threat of execution is the most common method of turning a captured agent (working for an intelligence service) into a double agent (working for a foreign intelligence service) or a double agent into a re-doubled agent. It is unlike a defector, who is not considered an agent as agents are in place to function for an intelligence service and defectors are not, but some consider that defectors in place are agents until they have defected.

Double agents are often used to transmit disinformation or to identify other agents as part of counter-espionage operations. They are often very trusted by the controlling organization since the target organization will give them true, but useless or even counterproductive, information to pass along.

Infiltrated the German Abwehr during World War II whilst feeding intelligence to MI5. He was so trusted by the Germans that he is reportedly the only British citizen to have ever been awarded the Iron Cross

Longtime head of KGB operations in the U.S., provided disinformation regarding American involvement in Prague Spring; and also played a role in the establishment of Yeltsin as post-USSR leader. Sentenced in absentia in 2002 to 15 years imprisonment; the US refuses to extradite him

Among other things, handed over the entire Swedish "FO-code", a top secret list of Sweden's defence establishments, coastal artillery fortifications and mobilization stores. Convicted in 79 and sentenced to life imprisonment for treason.

A re-doubled agent is an agent who gets caught as a double agent and is forced to mislead the foreign intelligence service.

F. M. Begoum describes the redoubled agent as "one whose duplicity in doubling for another service has been detected by his original sponsor and who has been persuaded to reverse his affections again".[2]